11-12 2.6-2.7 Binocular Balancing 1+2 (AC) PDF

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11 Lecture 2.6 | PRECLINICAL OPTOMETRY | Binocular Balancing 1 (Principals of Binocular Balancing Techniques) Lecture Objectives:   

To understand what is meant by the term binocular balancing To identify the types of patients that do and don’t need to be binocular balanced To detail the methods that may be employed to binocular balance your patient, and nominate the better method/s

Post-JCC: +/- 0.25 Sphere to Assess Monocular End Point   

Always work on following principle: o Maximum plus power (or least minus) consistent with best vision Px instructions are very important Occlude one eyeinstruct Px to view smallest line of letters on chart o Add +0.25DS (or +0.50/+1.00DS) to other eye o Ask Px “Is it clearer, just the same, or worse with this lens?”  Verify by getting them to read line of letter and check if worse o If clearer/just the same: add +0.25DS to monocular correction  Continue adding +0.25 until response is “worse” o If “worse” with +0.25DS then, and only then, try -0.25DS  With the -0.25 monocular correction, ask the Px:  “Is it clearer or smaller and darker with this lens?  If Px responds “clearer”verify they can read more letters on smaller lineif they can then add -0.25DS to monocular correction and repeat  If letters are “smaller and darker” do not add -0.25 (you’ve reached the spherical end point of monocular correction for this px)  Repeat this on the other eye

Additional Comments     

Observe Px o If they’re struggling, the lens probably made their VA worse Let Px know that it’s OK if both views look about the same o (ONLY when they start hesitating) If they’re hesitant, show them both views again With determination of astigmatic correction – encourage Px to select the best view Don’t keep bracketing the result – make a choice

What if VA is ≤ 6/9? 

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Pinhole o If VA improvement (PHVA)consider:  Uncorrected refractive error? (highly likely)  Paracentral media opacity?  Cortical cataract o If no VA improvement (NIPH)consider:  Did you do your refraction correct?  Amblyopia?  Pathology? Pinhole is good because it tells you if it’s a refractive error or a health problem PHVA  pin hole VA NIPH  no improvement pin hole

Why Some Patients Seem Uncertain as to What Lens Give Clearest Vision  

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The depth of focus can add uncertainty to a finite end point – hence if Px is undecided then follow “maximum plus minimum minus” Depth of focus varies with pupil size o DoF is larger for smaller pupils o Like how small aperture (big f number i.e. f22) = big depth of view for a camera Patients who are good at telling differences b/w glasses will be very appreciative when giving them even a small difference in refraction

Chromatic Aberration 

Shorter wavelengths brought to focus in front of longer wavelengths – in emmetropic eye blue is brought to focus in front of retina and red behind the retina when accommodation is relaxed

Red/Green Duochrome Test Chart  

Utilises the concept of chromatic aberration to find the refractive endpoint Green go plus, red stop minus

Instructions     

Reduce room illumination One eye occluded Are the letters/circles clearer or more prominent on the red side or green side or do they appear the same? If you’ve changed the power, ensure that VA has improved i.e. err on the side of more plus Beware if change VA by more than 0.50, especially in o Elderly o Hyperopes & pseudomyopes

How to Utilise the Chromatic Aberration of the Eye to Help Determine Monocular End Point of Refraction

+1.00 D Blur Check at End of Monocular Refraction    

Once you have completed the monocular refraction, you can check that a +1.00D lens blurs eye back to between ~6/12 – 6/15 Based on the rule that +0.25D will blur vision by one line +1.00D blurs ~4 lines i.e. from 6/4.8 to 6/12 or from 6/6 to 6/15 Used as a check that you haven’t over-minused” usually on a young Px with active accommodation

Principles of Binocular Balancing   

Very important to understand that you are attempting to balance or equalize the accommodation of the two eyes and not the VA If accommodation is not balanced, it will lead to symptoms and uncomfortable vision – by binocular balancing you are aiming to give comfortable & clear binocular vision The theoretical basis of binocular balancing techniques is that ocular accommodation is a consensual reflex o Means that any active accommodation in one eye will cause the same amount of accommodation in the other eye

When Binocular Balancing Is Not A Good Idea 

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When the Px doesn’t have any functional binocular vision – could be due to either o Strabismus  Px who got strabismus at an older age can’t have BB because they’ll have no binocular vision o Amblyopia o Pathology When there’s no active accommodation (e.g. elderly Px >60yo) In each case, attempt to get the same response from both eyes – use techniques that were used for monocular endpoint refinement

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The point of BB is to get even accommodation/relaxation in the two eyes

5 Basic Techniques of Binocular Balancing 1) 2) 3) 4) 5)

Successive alternate occlusion (with/without +0.50) Vertical prism dissociation (with/without +0.50 i.e. blur the Px) Blurring or Fogging techniques Septum techniques Polaroid techniques

Techniques 1-3 are the ones we’re going to learn and be familiar with. Technique 3 will be the one used most commonly. 1 or 2 should be the backup technique in case 3 doesn’t work.

Successive Alternate Occlusion (1)  Crude and relatively insensitive technique  Not a binocular technique  Used for Px with poor binocularity but where balancing might be advantageous o i.e. young hypermetropic anisometrope  Flip occluder from one eye to the other ask Px “which eye sees the clearer image?”use lenses (start with +0.50DS) to equalize vision o Can also use Duochrome if VA not too poor (i.e. better than 6/18)  Add +0.25 to the clearer eye until reversal is achieved

Vertical Prism Dissociation (2)  

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Not a very sensitive technique Not a binocular technique o Binocular vision isn’t stimulated because you’re stopping fusion from occurring Technique is unnatural and can be an uncomfortable viewing situation, however, used quite commonly TECHNIQUE o Use equal power vertical prisms (usually 2-3Δ D) of opposite base direction in front of each eye to vertically dissociate the images from the two yes (think of vertical fusional reserves) o Px is then asked to view 6/9 line (best to use single line of letters so less confusing to Px – e.g. drum of letters o Usually fog both eye when this technique is done by +0.50 added to both eyes The Px is asked to report if the letters are more distinct or easier to read on the upper or lower chart o If equally distinct, the accommodative state of the two eyes is considered to be balanced (may not be fully relaxed!) o If two lines are not equally distinct, a +0.25DS is added to the eye with the clearer vision and the test repeated o If you can’t achieve exact clarity, then give lenses that get closest to the equality of two lines – again aim to give maximum plus lens consistent with best vision

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What if Px doesn’t perceive two images? o Can try to cover/uncover one of the eyes o Can try to increase the prism amount Can also use Duochrome as the target o Px concentrates on each of the images separately and detects if red or green clearer o If exact green/red clarity cannot be achieved, just try to get one that’s closest to equality of two lines o Give maximum plus lens consistent with best vision o Means leave Px on the red side if you cannot equalize

E.g. if Rx is -2.00/-0.50 x 90 and -1.75/-0.75 x 90, and you needed -0.50 in the -2.00 eye then you’d give them -1.50/0.50 x 90 o As long as it’s within 0.50 then it’s fine. Anything more is most likely a ret technique problem.

Humphriss Fogging Technique  

Termed the psychological septum technique Initially designed by Humphriss in 1960 for use with Duochrome, but now more commonly used with letter chart and +/- 0.25D lenses

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Uses fog (blur) to suspend foveal vision in one eye but allows paracentral and peripheral vision to act as a binocular lock o Essentially fogs the macula so we don’t get see fine detail o Bino lock is when one eye looks at the target, and as such the other eye will also be looking at the same location (even though it’s fogged) Fog achieved with a +0.75DS or +1.00DS, but it is the level of fog (blur) that is important not the power of the lens

On completion of monocular refraction routine, you then fog (blur) one eye If 6/4.8 for eye under then fog other eye to 6/9 or 6/12 – so level of fog is 2 to 3 lines, to be certain this eye is not being used for critical vision o Power of lens to achieve this level of fog will vary between subjects ( but usually +0.75D to +1.00D) Will also vary if fogging dominant eye i.e may need more power HOWEVER if there’s too much fog then you’ll lose binocular lock o Always check which line the vision is fogged to With one eye fogged, Px is directed to line of best VA o Don’t tell Px you’ve fogged their eye though, they might close one eye which defeats the purpose of this test) Place +0.25D in front of unfogged eye and the Px is asked o “Does this lens make it clearer, just the same or actually worse” o Very important to ask “if just the same” because if Px is accommodating they will now relax 0.25D and the line will appear “just the same” If it is better or just the same, give Px +0.25D and repeat until the +0.25D makes it worse If +0.25D makes vision worse, then put -0.25 in front of unfogged eye and ask: “Does this lens make it clearer or just smaller and blacker?” o If balanced already, adding -0.25 will cause accommodation, which will cause letters to minify and make them “blacker” – Px often confuses this with “clearer” – so must ask px if the letters look smaller and blacker o Always leave +0.25D up for about 5 seconds so vision can stabilize and allow Px to relax any accommodation o With -0.25D should ask straight away Now fog the other eye, before removing the fog from the first eye, so that Px is not in full binocular state until end of test o Repeat procedure now on the previously fogged eye

Advantages of HFT   

Fully relaxes accommodation (doesn’t just equalize or balance accommodation) o Usually little need to do binocular addition after this Simple for Px and practitioner and quick to complete Although Px not given simultaneous binocular vision, because it’s simple and accurate therefore it’s a good technique to use

Humphriss Immediate Contrast (HIC) Technique • Alternative fogging (burring) technique which is sometimes used • With monocular findings in place a +1.00DS is placed before left eye and patient’s attention directed to end of 6/9 line • A +0.25DS is placed in front RE & then -0.25DS & patient is asked which is more ‘comfortable’. +ve lens always shown 1st • If correction already balanced +0.25DS will blur letters, while -0.25DS will stimulate 0.25D of accommodation but give a clear view – so will be preferred • Give -0.25DS to RE and repeat procedure. This time +0.25DS will not give rise to blurring as patient can relax the 0.25D accommodation. The -0.25DS will induce a further 0.25D accommodation (0.50D in total) and will not be as comfortable - consensual reflex means other eye would be 1.5D blurred so accommodation inhibited or uncomfortable. So, remove -0.25DS back at balanced correction. • When complete transfer fog to other eye and repeat. • Technique is more complex & relies on good subjective responses - so only use when have these

12 Lecture 2.7 | PRECLINICAL OPTOMETRY | Binocular Balancing 2 (Subjective Refraction: Binocular Balancing and the Final Prescription) Lecture Objectives: • To understand what is meant by the term binocular balance • To identify the types of patients that do and don’t need to be binocular balanced • To detail the methods that may be employed to binocular balance your patient, and nominate the better method/s • To review the steps of refraction • To talk about refining refraction/when to prescribe an Rx

5 Basic Techniques of Binocular Balancing 1) 2) 3) 4) 5)

Successive alternate occlusion (with/without +0.50) Vertical prism dissociation (with/without +0.50 i.e. blur the Px) Blurring or Fogging techniques Septum techniques Polaroid techniques

Humphriss Fogging Technique    

Termed the physiological septum technique Initially designed by Humphriss in 1960 for use with Duochrome, but now more commonly used with letter chart and +/- 0.25D lenses Uses fog (blur) to suspend foveal vision in one eye but allows paracentral and peripheral vision to act as a binocular lock Fog achieved with a +0.75D or a +1.00D but it is the level of fog (blur) that is important not the power of the lens

Septum and Polaroid Techniques    

Most sensitive techniques for binocular balancing, septum uses a physical barrier whilst polaroid has two different polaroid filters oriented differently in each eye Both work in same way by separating the central field of the two eyes while allowing paracentral and peripheral binocular vision The tests allow the most natural binocular viewing conditions o This is why they’re so sensitive However, not easy to set up with computer charts, and the Humphriss method/prism dissociation is consistent and reliable

6 Major Tests in Practice That Use the Septum or Polaroid Technique

Polarized Charts – Wilmut 

When a polarized lens is in front of both eyes, one will see the F and the other will see the L

Binocular Addition & Binocular Refraction Techniques Binocular Addition   

After completing your binocular balancing routine, the Px’s accommodation should be evenly balanced for the two eyes However, this doesn’t mean their accommodation is fully relaxes This is why you should always attempt a binocular addition at the end of your routine o i.e. at the end of your Humphriss/Prism technique, add +0.25 to make sure the Px’s accommodation is fully relaxed. The response you want to hear is that the vision is now worse, if it’s the same then the Px is a latent hyperope and you need to keep going until their vision is worse

Binocular Addition Technique 

Get Px to view binocularly the smallest line of letters they can see and place +0.25DS in front of both eyes simultaneously and ask the Px o “Are the letters clearer, just the same or actually worse (or more blurred) o If better or just the same, add +0.25DS to both eye’s correction o Keep going until you hit reversal (i.e. px says it’s worse) o After Px says it’s worse, can just put -0.25DS in front of both eyes, would expect to hear “just smaller and blacker” unless you’ve overplussed during balancing routine o Record final Rx & VA (could be different to previous monocular determination)

Binocular Refraction   

Refract under binocular conditions throughout your subjective refractive routine Eyes are in a more natural situation and accommodation will be more stable Negates the need for binocular balancing at end of your routine

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Particularly useful technique for younger patients and latent hyperopes as more effective at relaxing accommodation throughout the refraction routine

Binocular Refraction Technique       

Use Humphriss Fogging method After retinoscopic findings, one eye is fogged by +0.75 or +1.00D Carry out normal monocular routine on the other eye Important to check that fogging lens is effective in fogging 2 to 3 lines with respect to the other eye If retinoscopy findings very accurate then this technique won’t work Can adjust the focus of the other eye (because one eye is slightly fogged) o Can then do JCC and refine sphere Then transfer fog to other eye and repeat

Summary (Technique)  

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Retinoscopy Monocular Refraction o BVS o Determination of astigmatism o Check sphere o Determine for both eyes (OU) Binocular refraction – binocular balance Humphriss Fogging Technique Binocular push plus

What to Prescribe and When 

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Involve the patient in the decision o Compare your Rx with current glasses by using a trial frame or by placing lenses over their current glasses o If it ain’t broke don’t fix it – is the patient happy with their Rx?  Feel free to prescribe the refraction you find, keep it mind that it must improve their VA and that the change you are making is understood o Think about where and when the Px is going to use the glasses when you decide on the final Rx  I.e. just for driving, then slight over-minus might be OK  I.e. Does the Px need the full plus if they’re hyperopic and young? o Consider whether the Px’s hetrophoria influences your Rx  Sometimes different scripts may change a px’s phoria e.g. a certain script may be more normal for a certain script Don’t make tiny or huge changes in Rx o Don’t make huge changes in particular the near Rx An 0.50 equivalent sphere change will be appreciated by the Px, less than this amount is probably not significant o E.g. 0.50 sphere or 0.25/0.50 cyl

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Be careful with new anisometropic scripts and with cylindrical axis change Px with amblyopia my only require a balance lens in the poorer eye o Balance lens: A lens placed in a frame which looks like the lens for the opposite eye to balance cosmetics; similar in thickness and style with no specific Rx power. If a Px comes in with a sudden change (i.e. from 60 to 30 degrees) then check if it’s actually a change in 30 degrees or if it doesn’t exist o Was the previous optom wrong or perhaps you yourself got the wrong number? Prescribe when Px drives, they must be above a certain legal VA limit or when their uncorrected refractive error is bothersome (usually minimum is 0.50) Prescribe when Px has a near Rx of +0.75 in the other eye Prescribe based on Px symptoms and for prescbyopia when the px is ready (dw they’ll be back, it ain’t going anywhere)

Errors in Rx (Technique)     

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Incorrect prescribing Failure to adjust to a prescription Ocular pathology Communication Study by Cockburn 1980s: o Error rate 5% in about 1000 prescriptions although only about half were errors in prescription o Of the above, half were incorrect refractions initially about a quarter were because of image distortion and a quarter because of incorrect near working distance Other studies suggest about 2% of errors is average in dispensing specs o Therefore, a significant issue A study found that 80% of refractions were repeatable to 0.25 and 15% to 0.50 Biggest reason glasses not accepted is too strong a reading addition

Rx (How Much Before You Prescribe?) 

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Probably need about 1D of cyl before Px will notice Rx difference o Normally don’t prescribe -0.50, wait until they’re -0.75 (and if they’re young, they can be covered by accommodation anyway) o Hyperopia errors are generally higher than myopia errors Consider: o Amount of sphere in terms of myopia/hyperopia o Cyl o Presbyopia o Change o When to give a prescription o Do you have to give out the prescription? Keep it simple Maintain your patience Provide encouragement Proceed with a purpose – not too many choices...